Outdoor activities are very popular these days. During holidays many people have flocked to parks or forests to be close to nature for a change. Various types of outdoor furniture also have been developed and marketed to suit this trend, such as parasols, folding tables and chairs, portable cooking facilities and the like. Take parasol as an example. It mainly provides a shade area for people to rest and fend off sunshine. The conventional parasols mostly provide merely sunshade function. Some vendors now have tried to attach furniture to the parasol to improve its usability.
For instance, U.S. Pat. Nos. 7,134,762 and 7,497,583 disclose a light providing apparatus attachable to umbrella. The light providing apparatus includes a body, a clamping device, a light source and a power supply unit. The body has an inner wall and an opening to hold the umbrella. The clamping device is located on the inner wall facing the opening with a front end movable against the inner wall through a spring. Thus the light providing apparatus can be attached to the umbrella. Although the aforesaid technique provides a clamping structure installable on the umbrella, the holding strength of the clamping device on the umbrella depends on the elastic force of the spring. In the event that the elastic force weakens the clamping device cannot securely clamp the umbrella, then the light providing apparatus could be shaking against the umbrella. Moreover, the clamping device and the umbrella of the aforesaid technique are in contact with each other for merely a small area, hence it still leaves a lot to be desired in terms of the force for anchoring on the umbrella.